Illuminated graphic displays and buttons for automotive applications such as radios often have backlit insignia which identify the particular function of the display or button. Such backlit components have a light source which is positioned behind the insignia in order to make the insignia visible in the dark, necessitating that the insignia be capable of transmitting light from the light source.
A known process for manufacturing buttons and other backlit components is the use of paint and laser technology. These processes have generally involved the use of a transparent plastic substrate which may be painted white to form a white translucent layer over the transparent substrate, and then painted black to form an opaque black covering over the substrate and, if present, the white translucent layer. The black covering is then lased away to form an insignia. The transparent nature of the substrate maximizes the transmission of light through the backlit component for night time viewing. If present, the white translucent layer contributes graphics whiteness by reflecting light, such that the insignia is more readily visible under natural lighting conditions during daylight hours.
Numerous variations of the above structure exist. For example, U.S. Pat. No. 4,729,067 to Ohe teaches the use of a transparent substrate over which is sequentially deposited a translucent layer and a light diffusing layer. The translucent layer serves to bond the light diffusing layer to the transparent substrate, and enhance the diffusion of the light transmitted through the substrate into the light diffusing layer. However, the layers are delineated by chemically reacted surfaces, making the utilization of the teachings of Ohe rather complicated and expensive for mass production.
Another variation is disclosed in U.S. Pat. No. 3,694,945 to Detiker, which teaches the use of a white translucent substrate over which is formed an opaque grating composed of an opaque reflective layer and a translucent cover layer. The reflective layer serves to prevent light emitted from a light source beneath the substrate from reaching the covering layer, and then reflects the light back toward the substrate. Consequently, light emitted by the light source escapes only through openings in the grate. However, generating a grate in accordance with Detiker is relatively expensive and limits the use of such techniques to relatively large displays.
Paint and laser techniques of the type noted previously also have significant shortcomings. Insignias typically used in automobile graphic displays have a stroke width (the line width of the insignia) of only about 0.5 millimeter. Obtaining suitable optical characteristics with such intricate graphics requires very tight control of the cured thickness of the white paint in order to maintain the desired reflectance and transmissive properties. Often, as a result of the limitations of paint processes and paint chemistry, the thickness of the white paint must be maintained within a narrow range in order to achieve suitable lighting intensities for daytime and nighttime viewing. However, the variation in thickness between backlit components within a display group must be maintained within an even narrower range in order to provide a uniform lighting appearance.
Furthermore, the insignia of a backlit component formed in accordance with known methods will tend to have a nonuniform backlighting intensity unless the light transmitted to the component is appropriately and uniformly distributed over the entire area of the insignia. In practice, it is extremely difficult to achieve uniform distribution of light, which is typically accomplished with a light pipe whose geometry must be repetitively altered until a suitably uniform backlit intensity is achieved.
Even if uniform intensity is achieved within a single backlit component, differences in adjacent insignia often result in irregular illumination intensities within a backlit display group. This is particularly true with buttons of a backlit display which share one or more light sources. To minimize costs, such groupings often use a minimum number of light sources, and incorporate light pipes for the purpose of distributing the light energy equally to each of the backlit components. Though much effort has been directed toward optimizing the design of light pipes, uniform backlighting of each and every backlit component is very difficult due to size and location restraints. As a result, facets and painted patterns have often been applied to light pipes in order to increase the light intensity directed to relatively dim areas. Often, reflectors and additional lamps have been required, while excessively bright areas have been attenuated with printed halftone patterns behind the individual insignia.
While such tactics have been effective for flat screen printed displays, it is very costly and poorly suited for buttons and other backlit components which are not flat and have low lighting intensities. The above is further complicated where different shades or colors are desired for components within a backlit display group. As a result, lead times for developing a backlit display can be relatively long, adding undesirable development costs to the end product.
From the above, it can be seen that the prior art lacks a backlit component which can be readily produced to have a uniform and predictable backlit intensity. Accordingly, it would be desirable if a process existed by which a backlit component could be readily manufactured with minimal variability in backlighting intensity. Such a method would allow adjacent backlit components to be individually tailored to exhibit a suitable level of backlighting intensity when backlit by a minimal number of light sources.